1. Field of the Invention
This invention relates to an improved method of processing ores, and particularly phosphate ores. More particularly, the present invention relates to an improved method of conditioning slimes-containing phosphate ores before the flotation step of the beneficiation process.
2. Discussion of the Prior Art
Phosphate-containing ores, are normally concentrated, or beneficiated in a series of operations which result in a product having a higher content of phosphate values (e.g., 70% BPL), than the original ore. Normally, the ore is mined by removing the earth overburden from above the underground ore deposits, and then the ore is slurried with a water jet to form an aqueous slurry. The slurry is then transported, by any suitable means, e.g., a pipeline, to a beneficiation plant wherein the ore is screened to remove large size phosphate particles (larger than 3/4 inch). The undersize ore (particles smaller than 3/4 inch), in the aqueous pulp form, is subjected to screening and washing operations, to separate +1 mm. particles of the ore, called pebble. The -1 mm. size material is conducted to a downstream sizing step wherein the -150 mesh size material is removed to generate a substantially -1 mm. to +150 mesh size material. The -150 mesh size material, which is discarded as waste, is commonly referred to as "slimes". The -1 mm to +150 mesh size material is then subjected to a sizing operation to produce a -1 mm. to +35 mesh size fraction and a -35 to +150 mesh size fraction, commonly referred to as "conditioner feed", which are fed separately to the conditioning and flotation steps. The major portion of this material has the size within the 35-150 mesh size range. As used herein, the term "mesh size range" refers to standard Tyler screen mesh sizes.
In the conditioning step, this feed is contacted with chemical additives which aid in, in a downstream flotation step, in separating the phosphate particles from the contaminants, especially silica particles. The chemical additives typically used in the conditioning step are fatty acids, which sometimes have been previously saponified with alkali, and a hydrocarbon oil, such as fuel oil, see, for example, Tartaron, U.S. Pat. No. 2,105,826, Fenske, U.S. Pat. No. 2,922,522, Northcott, U.S. Pat. No. 3,032,197 and Snow U.S. Pat. No. 3,259,242. Water is also introduced into the conditioning step to obtain a slurry containing about 70% solids, and the slurry is vigorously mixed with the chemical additives and the water. The slurry is then conducted, after further water addition, to a flotation step wherein the phosphate particles are preferentially floated from silica and other contaminating particles.
The operations described above are called rougher conditioning and rougher flotation.
The previously-used conditioning and flotation process steps produced relatively low phosphate yields when they were used to process high slime ores. It is believed that the relatively low efficiency of the conditioning and flotation steps was due to the action of slimes, which, disproportionately to their total content in the ore, bound and thus wasted the chemicals used in the conditioning step. It is also believed that the vigorous mixing required in the conditioning step of the prior art produced a certain proportion of slimes (defined herein as extremely finely divided solid particles, some of which are inherently present with the phosphate ores and bound thereto by physical bonds). The conditioning step, as practiced heretofore, required such a vigorous agitation because it was necessary to thoroughly mix the relatively small amounts of the chemical additives, e.g., fatty acid and fuel oil, with a relatively large volume of water and phosphate ore (slurry) to substantially uniformly distribute the chemical additives in the slurry. During this vigorous mixing, it is believed, large amounts of slimes were formed because the vigorous mechanical mixing physically comminuted larger solid particles of the clays into smaller particles, thereby forming slimes. In addition, it is believed, vigorous mixing also contributed to the breaking of the physical bonds between the slimes, inherently associated with the phosphate ores, and the phosphate ore particles. Both of these mechanisms contributed to an increase in the total amount of slimes in the conditioning tanks. As is known to those skilled in the art, the slimes are responsible for relatively poor efficiency of the utilization of the additive chemicals used in the conditioning step of phosphate ore processing operations. The slimes, it is believed, through a chemical or physical mechanism or a combination of both, reduced the effectiveness of at least a portion of the hydrocarbon oil, thereby preventing it from performing the intended function of conditioning the phosphate ore for the flotation operation.
Accordingly, it is a primary object of the present invention to provide an improved process for processing phosphate ores.
It is an additional object of the present invention to provide a process of beneficiating phosphate ores which efficiently utilizes the chemical additives used in the conditioning and flotation steps of the beneficiation process.
Other objects of the invention will become apparent to those skilled in the art from the following description of the invention and the appended claims.